Polyester nanocomposites

ABSTRACT

Polyester nanocomposite compositions contain silica nanoparticles that have been subjected to surface treatment with novel trialkoxysilane compositions. The novel silane compositions are prepared by reacting a 3-isocyanatopropyl trialkoxysilane with 1,3-propanediol or certain polyether diols. The silica nanoparticles exhibit improved dispersion in the polyester. This leads to haze reduction and improvements in mechanical properties.

CROSS-REFERENCE TO RELATED APPLICATIONS

Subject matter disclosed herein is disclosed and claimed in thefollowing copending applications, filed contemporaneously herewith andassigned to the assignee of the present invention:

SURFACE-MODIFIED PARTICLES FOR POLYESTER NANOCOMPOSITES (Assignee docketnumber:CL 5126) U.S. Ser. No. ______; andSILANE COMPOSITIONS FOR POLYESTER NANOCOMPOSITES (Assignee docket numberCL4310) U.S. Ser. No. ______.

FIELD OF THE INVENTION

The present disclosure relates to polyester nanocomposites comprisingsurface-modified silica nanoparticles and a polyester.

TECHNICAL BACKGROUND OF THE INVENTION

Nanocomposites are polymers reinforced with nanometer sized particles,i.e., particles with a dimension on the order of 1 to several hundrednanometers. When nanoparticles are dispersed homogeneously throughoutthe polymer matrix, dramatic improvements in properties such asstrength, flexural and Young's modulus, heat distortion temperature, andbarrier to gas permeation can observed at very low filler loadings (<10%by weight). The nature and degree of property improvements depend inpart on the geometry of the nanoparticle, its surface chemistry, and itsinteraction with the polymer matrix. When the nanoparticles are notfully dispersed but are present as aggregates in the polymer matrix, thedesired property improvement may not be fully realized.

There remains a need for methods for preparing polyester nanocompositeshaving high dispersion of nanoparticles.

SUMMARY OF THE INVENTION

In one embodiment of the invention described herein, a composition isprovided described by Formula (I)

wherein each R¹ is independently a C₁₋₄ alkyl group; R² is an alkyleneor alkylene-ether group having a formula weight less than about 5000;and R³ is H, OH, or CH₃. In one embodiment, R² is the alkylene ethergroup —(CH₂)_((3+3n))O_(n)—,

wherein n=0 to about 85, and R³ is OH. This embodiment is described byFormula (II).

In another embodiment, a composition is provided comprising silica(SiO₂) particles whose surface is modified with a Formula (II) compoundwherein n=0 to 85.

In a further embodiment, a nanocomposite composition is providedcomprising a polyester and silica nanoparticles whose surface ismodified with a compound described by Formula (II) wherein n=0 to 5.

The invention further provides processes for preparing saidcompositions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a transmission electron micrograph of a poly(propyleneterephthalate) nanocomposite containing silica nanoparticlessurface-modified with ICPTES-Polyol 3 (Example 3, Sample 3B),illustrating good nanoparticle dispersion.

FIG. 2 is a transmission electron micrograph of a poly(propyleneterephthalate) nanocomposite containing silica nanoparticlessurface-modified with N-(3-triethoxysilylpropyl)-4-hydroxybutyramide(Comparative Example B), illustrating poor nanoparticles dispersion.

DETAILED DESCRIPTION OF THE INVENTION

In the context of this disclosure, a number of terms shall be utilized.

As used herein, the term “nanocomposite” or “polymer nanocomposite”means a polymeric material which contains particles, dispersedthroughout the polymeric material, having at least one dimension in the0.1 to 100 nm range (“nanoparticles”). The polymeric material in whichthe nanoparticles are dispersed is often referred to as the “polymermatrix.” The term “polyester composite” refers to a nanocomposite inwhich the polymeric material includes at least one polyester.

As used herein, the term “alkyl” means a univalent group derived from analkane by removing a hydrogen atom from any carbon atom: —C_(n)H_(2n+1)where n≧1.

As used herein, “an alkylene group” means the divalent group—C_(n)H_(2n)— where n≧1.

As used herein, the term “alkylene-ether” means an alkylene group havingat least one in-chain ether oxygen. One example is —CH₂—CH₂—O—. Anotherexample is —(CH₂)_((3+3n))O_(n)—,

As used herein, “polyester” means a condensation polymer in which morethan 50 percent of the groups connecting repeat units are ester groups.Thus polyesters may include polyesters, poly(ester-amides) andpoly(ester-imides), so long as more than half of the connecting groupsare ester groups. Preferably at least 70% of the connecting groups areesters, more preferably at least 90% of the connecting groups are ester,and especially preferably essentially all of the connecting groups areesters. The proportion of ester connecting groups can be estimated to afirst approximation by the molar ratios of monomers used to make thepolyester.

As used herein, “diol component” means a compound from which diol repeatunits in the polyester are generated. For example, for poly(ethyleneterephthalate), the diol component would be ethylene glycol.

As used herein, “acid component” means a compound from which acid repeatunits in the polyester are generated. For example, for poly(ethyleneterephthalate), the acid component would be terephthalic acid ordimethyl terephthalate.

Silanes

In one embodiment of the invention described herein, a composition isprovided described by Formula (I)

wherein each R¹ is independently a C₁₋₄ alkyl group; R² is an alkyleneor alkylene-ether group having a formula weight less than about 5000;and R³ is H, OH, or CH₃. In some embodiments, the formula weight of R²is between and optionally including any two of the following values: 14(i.e., when R² is —CH₂—), 100, 200, 300, 400, 500, 600, 700, 800, 900,1000, 1200, 1500, 2000, 2500, 3000, 4000, and 5000.

The composition is prepared by reacting a compound described by Formula(III)

(i.e., a 3-isocyanatopropyl trialkoxysilane, “ICPTAS”) with HO—R²—R³. Inan embodiment, HO—R²—R³ is the composition described by Formula (IV)

wherein n=0 to about 85. In some embodiments, n is between andoptionally including any two of the following values: 0, 1, 2, 3, 4, 5,6, 7, 8, 9, 10, 15, 20, 25, 35, 45, 55, 65, 75, and 85.

When HO—R²—R³ is the composition is described by Formula (IV), theproduct of its reaction with the ICPTAS is the composition described byFormula (II).

In one embodiment, the composition described by Formula (III) is

3-isocyanatopropyl triethoxysilane (“ICPTES”). ICPTES is availablecommercially, e.g., from Gelest, Inc. (Morrisville, Pa., USA).

When n=0, the Formula (IV) composition is 1,3-propanediol, which isavailable commercially, e.g., from Sigma-Aldrich (St. Louis, Mo., USA).When n is nonzero, Formula (IV) describes a “polyol” (i.e., a polyetherdiol) of 1,3-propanediol. Polyols of 1,3-propanediol with molecularweight from about 500 (n=7) to about 3000 are available commercially,e.g., from E. I. du Pont de Nemours & Co. (Wilmington, Del., USA), underthe trade name DuPont™ Cerenol™ polyols. Polyols of 1,3-propanediol withlower molecular weight than 500 can be prepared by methods described in,e.g., E. C. Knuf et al. (Journal of Organic Chemistry, (2003), 68 (23),9166-9169) and S. M. Gurvich and R. Ya. Sokolova (Zhurnal OrganicheskoiKhimii, (1965), 1 (3), 500-502).

The reaction between the ICPTAS and HO—R²—R³ is carried out in theabsence of oxygen in a nonprotic, anhydrous solvent in which it issufficiently soluble, as indicated by the clarity of the mixture ofHO—R²—R³ and solvent. For example, diethyl ether can be used as asolvent when HO—R²—R³ is the composition described by Formula (IV)wherein n=0 to about 16. The ICPTAS and HO—R²—R³ are reacted in a 1:1 to1:1.2 molar ratio. In one embodiment, the reaction is carried outwithout a catalyst. In another embodiment, the reaction is carried outthe presence of a catalyst such as dibutyltin dilaurate or a tertiaryamine (e.g., triethylamine). Typically, the reaction is carried outunder ambient conditions over several hours. In one embodiment, whereinHO—R²—R³ is the composition described by Formula (IV), the reactiontemperature is about 0° C. to about 25° C. and the reaction time isabout 4 hours to about 24 hours. The solvent is then removed by anyconvenient means, such as by applying a vacuum.

The silane compositions generally described by Formula (I) can be usedto modify the surface characteristics of substrates onto which they arecoated, particularly inorganic surfaces having hydroxyl groups that canbe converted to stable oxane bonds by reaction with the silane. Forexample, they can be used to make a surface more hydrophobic. Thus,masonry can be rendered water repellent and glass surfaces of treatedmetal-glass capacitors can exhibit reduced electrical leakage in humidconditions. Laboratory glassware such as pipettes and graduatedcylinders so treated can completely transfer aqueous solutions. Gaschromatography packing of diatomaceous earth or silica so treated canexhibit reduced tailing in use. The silane compositions materialsgenerally described by Formula (I) can be utilized in composites,adhesives, sealants, and coatings. They can be used to modify thesurfaces of inorganic oxygen-containing materials, including but notlimited to silica, silicates, borosilicates, aluminosilicates, days, andmetal oxides.

Silica Surface Modification

In an embodiment of the invention described herein, a composition isprovided comprising silica particles whose surface is modified with acompound described by Formula (I) wherein each R¹ is independently aC₁₋₄ alkyl group; R² is an alkylene or alkylene-ether group and having aformula weight less than about 5000; and R³ is H, OH, or CH₃. In oneembodiment, each R¹ is independently ethyl or methyl, R² is the alkyleneether group

—(CH₂)_((3+3n))O_(n)—, i.e.,

wherein n=0 to about 85, and R³ is OH. In one such embodiment, thesilica particles are nanoparticles. In some embodiments, n is between(and optionally including) any two of the following values: 0, 2, 5, 10,20, 30, 40, 50, 60, 70, 80, and 85. The surface modified particles areprepared from an aqueous colloidal silica dispersion, which is anaqueous dispersion of amorphous silica particles having diameters ofabout 1 to about 150 nm. Preparation and properties of colloidal silicadispersions are described by H. E. Bergna in Colloidal silica:fundamentals and applications (Surfactant science series, v. 131), H. E.Bergna and W. O. Roberts eds., CRC Press (1996), pp. 9-35. The SiO₂concentration of suitable dispersions are typically about 15 to about 50wt % SiO₂ in water and are commercially available, e.g., from W. R.Grace & Company (Columbia, Md., USA), Ondeo Nalco (Naperville, Ill.,USA), and Sigma-Aldrich (St. Louis, Mo., USA). In some embodiments, theSiO₂ concentration is between (and optionally including) any two of thefollowing values: 15, 20, 25, 30, 35, 40, 45, and 50.

The aqueous dispersion containing the silica nanoparticles is solventexchanged with a diol or mixture of diols to produce a colloidalsilica/diol dispersion. In one embodiment, where the intended use of theparticles is dispersion in a polyester to form a nanocomposite, the diolused can be the diol component of the polyester matrix, e.g.,1,3-propanediol (“PDO”) for the polyester poly(propylene terephthalate);where the polyester is a blend (physical mixture) or copolymer (chemicalmixture) of two or more polyesters, a mixture of the diol components ofthe polyesters can be used. Water is then removed from the dispersion byany convenient method, e.g., by boiling under vacuum.

The compound described by Formula (I) is then added to the colloidalsilica/diol dispersion to form a mixture wherein the surface coverage ofthe silica particles is about 0.25 to about 4 molecules of Formula (I)compound per nm² silica particle surface. The amount of Formula (I)compound added to achieve this coverage will depend on silica particlesize and geometry and the molecular weight of the Formula (I) compound.When the formula weight of R² in the Formula (I) compound is less thanabout 1000 and the silica particles are spherical nanoparticles, atypical amount is about 0.08 g to 0.15 g of Formula (I) compound pergram of silica.

The mixture is then heated at a temperature in the range from about 60°C. to about 215° C. for about 5 minutes to about 2 hours to react theFormula (I) compound with the silica surface; in one embodiment, themixture is heated at about 100° C. for about 30 minutes. Optimum timeand temperature for specific Formula (I) compounds and silica particlesare readily determined by one having ordinary skill in the art.

Nanocomposites

In a further embodiment, a composition is provided comprising apolyester and silica nanoparticles dispersed therein, wherein thesurface of the silica nanoparticles is modified with a compounddescribed by Formula (II) wherein each R¹ is independently ethyl ormethyl, R² is the alkylene ether group

—(CH₂)_((3+3n))O_(n)—, i.e.,

wherein n=0 to about 5, and R³ is OH. The surface modification allowspolyester nanocomposites to be prepared in which the nanoparticles arevery well dispersed. In one embodiment, the polyester is poly(ethyleneterephthalate) (PET), poly(ethylene isophthalate), poly(propyleneterephthalate) (PPT), poly(butylene terephthalate) (PBT), a physicalmixture of at least two of these; or a polyester copolymer whose diolcomponent is at least two diols selected from ethylene glycol,1,3-propane diol and 1,4-butanediol, and whose acid component isterephthalic acid (or, equivalently, dimethyl terephthalate) and/orisophthalic acid (or, equivalently, dimethyl isophthalate).

The nanocomposite is prepared by in situ polymerization, that is,polymerization of the polyester in the presence of a dispersion of thesurface-treated silica nanoparticles in a diol or diol mixturecorresponding to the diol component of the polymerized polyester. Forexample, to prepare a nanocomposite of PPT and silica nanoparticles, thesilica nanoparticles would be introduced into the polymerization mixtureas a dispersion in 1,3-propane diol. If the polyester is to be acopolymer, for example, of poly(butylene terephthalate) andpoly(ethylene terephthalate), the silica nanoparticles would beintroduced into the polymerization mixture as a dispersion in a mixtureof 1,4-butanediol and ethylene glycol. Suitable methods of polyesterpolymerization are described in U.S. Published Patent Application2009/0192254 which is hereby incorporated in its entirety for allpurposes.

The polymerization process may be carried out in any way known in theart. For example it may be a batch, semibatch or continuous process.Both these types of processes are will known in the art; see A. J. East,et al. in the Kirk-Othmer Encyclopedia of Chemical Technology, JohnWiley & Sons, J. I. Kroschwitz exec. ed., 4^(th) edition (1996), vol.19, 609-653. For commercial use, a continuous process is preferred.Another process variation is melt polymerization of the polyesterprecursors to a polyester whose molecular weight is suitable forso-called solid state polymerization, and then subjecting this polyesterto solid state polymerization to achieve the desired molecular weight.

Other materials may also optionally be present during the polymerizationprocess, such as stabilizers, antioxidants, and other materialssometimes added to such processes. Other filler(s) and/or reinforcingagent(s) may also be present in the polymerization, either from thebeginning of the process or added during the process as long as they donot interfere with the polymerization itself.

The polyester nanocomposites described herein are characterized byimproved dispersion of silica nanoparticles throughout the polyestermatrix in comparison with analogous compositions containing silicananoparticles whose surfaces have not been modified with a compounddescribed by Formula (I). This is illustrated in FIGS. 1 and 2. FIG. 1is a transmission electron micrograph of a poly(propylene terephthalate)nanocomposite containing silica nanoparticles surface-modified withICPTES-Polyol 3 (Example 3, Sample 3B) in accordance with the presentinvention, illustrating good nanoparticle dispersion. FIG. 2 is atransmission electron micrograph of a poly(propylene terephthalate)nanocomposite containing silica nanoparticles surface-modified withN-(3-triethoxysilylpropyl)-4-hydroxybutyramide (Comparative Example B),not according to the present invention, illustrating poor nanoparticledispersion. The improved dispersion results in mechanical propertyimprovement in molded samples and reduced haze in film.

Articles comprising the polyester nanocomposite compositions produced bythe present invention may be prepared by any means known in the art,such as, but not limited to, methods of injection molding, extrusion,blow molding, thermoforming, fiber spinning, or film blowing. Thepolyester nanocomposite compositions may be the form of, for example,film, sheet, containers, membranes, laminates, pellets, coatings, foam,monofilament fiber and multifilament yarn. The polyester nanocompositecompositions may be blended with ingredients such as flame retardants,plasticizers, pigments, other polymers (for example, polycarbonate)various rubber tougheners, and the like as needed. Many suitableadditives are described in U.S. Published Patent Application2009/0192254 which is hereby incorporated in its entirety for allpurposes.

The polyester nanocomposite materials produced as described herein canbe used in articles of manufacture in a wide variety of applications,including without limitation articles for: electrical and electronicapplications, such as electrical connectors, plugs, switches, keyboardcomponents, printed circuit boards, electronic cabinets and housingssuch as personal computer housings, printer housings, peripheralhousings, server housings, and small electric motor components;automotive applications, such as distributor caps, coil-formers, rotors,windshield wiper arms, headlight mountings, and other fittings, fenders,fascia, hoods, tank flaps and other exterior parts and interiorautomotive panels; control panels, chassis (cases); exterior andinterior panels for vehicles such as trains, tractors, lawn mower decks,trucks, snowmobiles, aircraft, and ships; decorative interior panels forbuildings; furniture such as office and/or home chairs and tables;industrial machinery, for example in molded conveyor-belt links; medicaldevices, such as nasal sprays and nebulizers; home appliances, such asfood mixers, hair dryers, coffee makers, washing machine tubs andexterior parts, appliance handles, interior and exterior refrigeratorpanels, dishwasher front and interior panels and toasters; power toolhousings such as drills and saws; and a variety of other applications,such as fiber-optical cable buffer tubes, countertops, camera parts,telephones, cell phones, and related equipment.

Polyester monofilaments are used as reinforcements for rubber articles,fishing lines, toothbrush bristles, paintbrush bristles and the like,and in industrial applications such as tire cords, composites, belts,and textiles. In addition, woven fabrics produced from monofilaments areused, for example, in industrial belts and paper machine clothing.Multifilament yarns can be produced comprising the polyester compositesdescribed herein using any of the typical processes well known in theart for making multifilament polyester yarns. Monofilaments andmultifilament yarns can be woven into textile fabrics, using knownprocesses.

Where a range of numerical values is recited herein, unless otherwisestated, the range is intended to include the endpoints thereof, and allintegers and fractions within the range. It is not intended that thescope of the invention be limited to the specific values recited whendefining a range.

EXAMPLES

The present invention is further defined in the following Examples. Itshould be understood that these Examples, while indicating preferredembodiments of the invention, are given by way of illustration only.From the above discussion and these Examples, one skilled in the art canascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various uses andconditions.

The meaning of abbreviations is as follows: “BDO” means 1,4-butanediol,“DBTDL” means dibutyltin dilaurate, “DMA” means dynamic mechanicalanalysis, “g” means gram(s), “GPC” means gel permeation chromatography,“h” means hour(s), “ICPTES” means 3-isocyanatopropyl triethoxysilane,“ICPTMS” means 3-isocyanatopropyl trimethoxysilane “min” meansminute(s), “mL” means milliliter(s), “M_(n)” means number averagemolecular weight, “MPa” means megapascal(s), “mtorr” means millitorr,“M_(w)” means number average molecular weight, “PBT” means poly(butyleneterephthalate). “PDO” means 1,3-propanediol, “PPT” means poly(propyleneterephthalate), “rpm” means revolutions per minute, “TEM” meanstransmission electron microscopy, “T_(g)” means glass transitiontemperature, “T_(m)” means melting temperature, “T_(HC)” meanscrystallization temperature from the melt, “wt %” means weightpercent(age), “ΔH_(c)” means heat of crystallization, and “μL” meansmicroliter(s).

Methods

Transmission electron microscopy was used to assess dispersion quality.

Molecular weights were measured by gel permeation chromatography.

Thermal transitions (glass transition (T_(g)), melting temperature(T_(m)), and the crystallization temperature from the melt (T_(HC)) andpercent crystallinity (by the heat of crystallization, ΔH_(C)) weremeasured by differential scanning calorimetry.

Haze was measured by UV/visible spectrophotometry using ASTM D-1003,Procedure B (unidirectional illumination with diffuse viewing). Theinstrument used was Varian Cary 5000 uv/vis/nir spectrophotometerequipped with a DRA 2500 diffuse reflectance accessory (150 mmintegrating sphere).

Tensile modulus, tensile strength and elongation at break weredetermined on tensile bars conforming to ISO 527-1 titled“Plastics—Determination of tensile properties.” Measurements were doneat room temperature. Testing was carried out in accordance with ISO527-1 specifications.

Storage modulus (flexural) at elevated temperature was determined bydynamic mechanical analysis (DMA).

Materials

LUDOX® TMA colloidal silica, 34 wt % suspension in water;1,3-propanediol, (99.6+% purity); dimethylene terephthalate (99+%purity); and 1,4-butanediol (99% purity, Reagent plus grade) werepurchased from Sigma-Aldrich® (St. Louis, Mo., USA).

3-Isocyanatopropyl triethoxysilane (95% purity), 3-isocyanatopropyltrimethoxysilane (95% purity),N-(3-triethoxysilylpropyl)-4-hydroxybutyramide,bis(2-hydroxyethy)-3-aminopropyl triethoxysilane (62% in ethanol), andaminopropyl triethoxysilane (99+% purity) were purchased from Gelest,Inc. (Morrisville, Pa., USA).

Tyzor® TPT catalyst was obtained from E. I. du Pont de Nemours & Co.,Inc. (Wilmington, Del., USA).

N-propanol (99.99% purity, OmniSolv® high purity solvent) was obtainedfrom EMD Chemicals (Gibbstown, N.J., USA).

Samples of the Polyether Diol

having molecular weight about 250 g/mol (n=3) and about 500 g/mol (n=7)were also obtained from the DuPont Company and are referred to herein as“Polyol 3” and “Polyol 7”, respectively.

Example 1 Synthesis of Silanes

1,3-Propanediol (PDO), and 3-isocyanatopropyl triethoxysilane (ICPTES)were reacted in a 1:1 molar ratio to form ICPTES-PDO (Formula (II)wherein R¹ is ethyl and n is zero). Inside a nitrogen-filled glove boxat ambient temperature, 3.05 g (0.04 mol) of PDO was added to a 250 mLround bottom flask with stirring bar. 40 mL of diethyl ether was addedto the flask and the contents were stirred, forming a solution. To thissolution was added 9.895 g (0.04 mol) of ICPTES slowly, followed by 76μL (1.2×10⁻⁴ mol) of catalyst dibutyltin dilaurate (DBTDL). The reactionmixture was allowed to stir overnight. The next day, the solvent wasstripped off in the glove box.

9.895 g (0.04 mol) ICPTES was similarly reacted with 0.04 mol of:

Polyol 3 to form ICPTES-Polyol 3 (Formula (II) wherein R¹ is ethyl and nis 3); and

Polyol 7 to form ICPTES-Polyol 7 (Formula (II) wherein R¹ is ethyl and nis 7).

Similarly, 14.842 g (0.072 mol) 3-isocyanatopropyl trimethoxysilane(ICPTMS) was reacted with 0.06 mol of N-propanol to formICPTMS-n-propanol (Formula (I) wherein R¹ is ethyl, R² is —(CH₂)₂— andR³ is CH₃); and 0.06 mol of ICPTMS was reacted with 0.05 mol of1,4-butanediol to form ICPTMS-BDO (Formula (I) wherein R¹ is ethyl, R²is —(CH₂)₄— and R³ is OH).

Example 2 Colloidal Silica Solvent Exchange and Surface Modification

221.3 g aqueous colloidal silica dispersion (Ludox® TMA, 34 wt % silica)was mixed with 250 mL 1,3-propanediol (PDO). The water was boiled offfrom the mixture under vacuum. A transparent colloidal silica dispersionin PDO was obtained. 7.86 g ICPTES-PDO was then added to the colloidalsilica PDO dispersion. The mixture was then heated at 100° C. for 30 minto react ICPTES-PDO onto the surface of silica nanoparticles.

The wt % of silica in the ICPTES-PDO treated silica PDO colloidaldispersion was measured to be 22.2 wt % by firing the sample at 600° C.for 12 hours. The amount of water in dispersion is 0.3144% measured byKarl Fisher titration.

This method was also used to prepare silica nanoparticles with thefollowing surface treatments: ICPTES-Polyol 3, ICPTES-Polyol 7,ICPTMS-BDO, ICPTMS-n-propanol, bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane, N-(3-triethoxysilylpropyl)-4-hydroxybutyramide, andICPTES itself.

Example 3 Polymerization of PPT in the Presence of Surface Treated SiO₂

Dimethylterephthalate (134.17 g, 0.69 mol), 1,3-propanediol (68.46 g,0.90 mol), and a colloidal dispersion of 22.2 wt % surface treatedsilica in PDO (33.78 g, surface treatment with ICPTES-PDO) prepared asin Example 2 were charged to a 500 mL three-necked round bottom flask.An overhead stirrer and a distillation condenser were attached. Thereaction mass was kept under a N₂ purge atmosphere. The contents weredegassed three times by evacuating down to 500 mtorr and refilling backwith N₂ gas. The flask was immersed in a preheated metal bath set at160° C. The solids were allowed to completely melt at 160° C. and thestirrer speed was slowly increased to 180 rpm. 67 μL of catalyst Tyzor®TPT was added under a N₂ blanket. The temperature was increased to 210°C. The system was maintained at 210° C. for 60 minutes to distill offmost of the methanol produced. The temperature was increased to 250° C.and was held constant for 30 minutes. The nitrogen flush was closed offand vacuum ramp was started. After 36 min, the vacuum reached a value of55 mtorr. The reaction was maintained under vacuum for approximately 41min. Molecular weight, thermal analyses, and ash content of thenanocomposite thereby produced (“3A”) are presented in Table 1.

PPT nanocomposites were similarly prepared using colloidal dispersionsof silica nanoparticles that had been surface-treated with ICPTES-Polyol3 (3B), ICPTES-Polyol 7 (3C), ICPTMS-BDO (3D), and ICPTMS-n-propanol(3E). Analyses of the nanocomposites thereby produced are presented inTable 1.

Comparative Example A Polymerization of PPT in the Presence of SiO₂Articles without Surface Treatment

Example 3 was repeated except that the silica particles had not beensurface treated. Molecular weight, thermal analyses, and ash content ofthe nanocomposite thereby produced are presented in Table 1.

Comparative Example B Polymerization of PPT in the Presence of SiO₂Surface Treated with N-(3-triethoxysilylpropyl)-4-hydroxybutyramide

Dimethylterephthalate (134.17 g, 0.69 mol), 1,3-Propanediol (68.89 g,0.90 mol) and 33.35 g of 22.5% colloidal surface treated silica in PDO(surface treatment with N-(3-triethoxysilylpropyl)-4-hydroxybutyramide)were charged to a 500 mL three necked round bottom flask. An overheadstirrer and a distillation condenser were attached. The reaction masswas kept under N₂ purge atmosphere. The contents were degassed threetimes by evacuating down to 500 mtorr and refilling back with N₂ gas.The flask was immersed in a preheated metal batch set at 160° C. Thesolids were allowed to completely melt at 160° C. and the stirrer speedwas slowly increased to 180 rpm. 67 μL of catalyst Tyzor® TPT was addedunder a N₂ blanket. The temperature was increased to 210° C. The systemwas maintained at 210° C. for almost 2 hours to distill off most of themethanol produced. The temperature was increased to 250° C. and was heldconstant for 30 minutes. The nitrogen flush was closed off and vacuumramp was started. After 29 min, the vacuum reached a value of 52 mtorr.The reaction was maintained under vacuum for approximately 1 h and 43min. Molecular weight, thermal analyses, and ash content of thenanocomposite thereby produced are presented in Table 1.

Comparative Example C Polymerization of PPT in the Presence of SiO₂Surface Treated with bis(2-hydroxyethy)-3-aminopropyl triethoxysilane

Example 3 was repeated except that the silica particles had been surfacetreated with bis(2-hydroxyethy)-3-aminopropyl triethoxysilane. Molecularweight, thermal analyses, and ash content of the nanocomposite therebyproduced are presented in Table 1.

Comparative Example D Polymerization of PPT in the Presence of SiO₂Surface Treated with ICPTES

Example 3 was repeated except that the silica particles had been surfacetreated with ICPTES. Particle dispersion as determined by TEM was poor(Table 2).

TABLE 1 % Crystallinity Ash T_(g) T_(m) T_(HC) as made, by GPC analysisSample (wt %) (° C.) (° C.) (° C.) ΔH_(C) (g/mol) Comp. 4.72 55 229 16330.8 M_(n) = 24200 Ex. A M_(w) = 45800 Comp. 5.25 53 229 167 30.6 M_(n)= 20600 Ex. B M_(w) = 44500 Comp. 5.05 56 229 167 30.6 M_(n) = 20200 Ex.C M_(w) = 39000 3A 4.92 53 228 166 32.7 M_(n) = 21300 M_(w) = 45000 3B4.92 56 228 168 34.4 M_(n) = 24200 M_(w) = 45800 3C 5.00 54 229 168 33.9M_(n) = 24200 M_(w) = 45800

Example 4 Dispersion Quality of Silica in PPT Nanocomposites

Samples of the nanocomposites prepared in Example 3 and ComparativeExamples A, B, and C were examined using transmission electronmicroscopy (TEM) to assess the quality of the dispersion of the silicaparticles. A representative example of “good” dispersion (Example 3B) ispresented in FIG. 1. A representative example of “poor” dispersion(Comparative Example B) is presented in FIG. 2. Haze measurements werealso used to assess dispersion quality of several samples, lower hazeindicating better dispersion. Results are summarized in Table 2.

TABLE 2 Dispersion Haze, Quality Sample Silica Surface Treatment % byTEM Comp. none 88 Poor Ex. A Comp. Ex. B

95.3 Poor Comp. Ex. C

94.5 Poor Comp. Ex. D

89.2 Poor 3A

20.8 Good 3B

23.4 Good 3C

85.4 Poor 3D ICPTMS-BDO Good 3E ICPTMS-n-propanol 24.5 Good

Example 5 Polymerization of PBT in the Presence of SiO₂ Surface Treatedwith ICPTES-BDO

Dimethylterephthalate (110.86 g, 0.57 mol), 1,4-butanediol (BDO) (85.47g, 0.95 mol) and 22.6% colloidal surface treated silica in PDO (surfacetreatment with ICPTES-BDO, 26.47 g) were charged to a 500 mL threenecked round bottom flask. An overhead stirrer and a distillationcondenser were attached. The reaction mass was kept under N₂ purgeatmosphere. The contents were degassed three times by evacuating down to500 mtorr and refilling back with N₂ gas. 145 μL of catalyst Tyzor®TnTBT was added under a N₂ blanket after the first evacuation. The flaskwas immersed in a preheated metal bath set at 160° C. The solids wereallowed to melt completely at 160° C. and the stirrer speed was slowlyincreased to 180 rpm. The temperature was increased to 225° C. Thesystem was maintained at 225° C. for 40 minutes to distill off most ofthe methanol. The temperature was increased to 250° C., the nitrogenflush was closed off and vacuum ramp was started. The reaction wasmaintained under vacuum for approximately 60 min. Analytical results:M_(n)=31300 g/mol, M_(w)=77400 g/mol, T_(g)=42° C., T_(m)=222° C., andT_(HC)=186° C. The inorganic silica content as determined by ashanalysis was found to be 4.56 wt %. TEM indicated dispersion quality wasexcellent.

Example 6 Mechanical Properties of Silica/PPT Nanocomposites

Mechanical properties of samples prepared in Example A, Example B,Example C, Comparative Example A, Comparative Example B, and ComparativeExample C were measured as described above and are presented in Table 3.

TABLE 3 Flexural Flexural Tensile Tensile Modulus Modulus ModulusStrength Elongation E(100° C.) E(205° C.) Example Dispersion (MPa) (MPa)(%) MPa MPa Comp. Poor 2806.2(85.6) 48.1(8.1) 1.9(0.4) 512.6 343.0 Ex. AComp. Poor  2935.4(163.3) 31.4(3.4) 1.1(0.1) 356.1 202.3 Ex. B Comp.Poor 2864.2(74.1) 29.5(4.9) 1.1(0.2) 388.8 335.9 Ex. C 3A Good2784.6(57.2) 55.3(2.9) 2.3(0.2) 567.7 372.2 3B Good 2776.8(61.4)49.5(8.4) 2.0(0.4) 408.5 303.5 3C Poor  2778.0(133.1) 41.2(8.0) 1.6(0.4)422.5 278.4

Statistical Analysis

Tensile strength: A comparison of the combined data for the four sampleswith poor dispersion with the combined data for the two samples withgood dispersion shows that there is a statistically significantdifference between the two groups:

Two-sample T test for Poor Dispersion vs. Good Dispersion Mean TensileDispersion N Strength StDev SE Mean Poor 16 37.55 9.66 2.4 Good 8 52.376.57 2.3

Difference=mu(Poor dispersion)−mu(Good dispersion)

Estimate for difference: −14.8295% CI for difference: (−21.83, −7.81)T-Test of difference=0 (vs. not=): T-Value=−4.42, DF=19, P-Value=0.000%

% Elongation: A comparison of the combined data for the four sampleswith poor dispersion with the combined data for the two samples withgood dispersion shows that there is a statistically significantdifference between the two groups:

Two-sample T test for Poor Dispersion vs. Good Dispersion Mean %Dispersion N Elongation StDev SE Mean Poor 16 1.418 0.457 0.11 Good 82.158 0.354 0.13

Difference=mu(Poor Dispersion)−mu(Good Dispersion)

Estimate for difference: −0.73995% CI for difference: (−1.097, −0.382)T-Test of difference=0 (vs. not=): T-Value=−4.36, DF=17, P-Value=0.000

Modulus: A comparison of the combined data for the four samples withpoor dispersion with the combined data for the two samples with gooddispersion shows that there is not a statistically significantdifference in room temperature tensile modulus between the two groups(t-test P=0.089). A similar lack of statistical significance was foundfor flexural modulus by DMA at elevated temperatures.

1. A composition comprising a polyester and silica nanoparticlesdispersed therein, wherein the surface of the silica nanoparticles ismodified with a compound described by Formula (II)

wherein each R¹ is independently ethyl or methyl and n=0 to about
 5. 2.The composition of claim 1 wherein the polyester is poly(ethyleneterephthalate), poly(ethylene isophthalate), poly(propyleneterephthalate), poly(butylene terephthalate), a physical mixture of atleast two of these; or a polyester copolymer whose diol component is atleast two diols selected from ethylene glycol, 1,3-propane diol and1,4-butanediol, and whose acid component is terephthalic acid or,equivalently, dimethyl terephthalate, and/or isophthalic acid or,equivalently, dimethyl isophthalate.
 3. An article of manufacturecomprising the composition of claim
 1. 4. A process for preparing acomposition of claim 1 comprising polymerizing the polyester in thepresence of the silica nanoparticles.